Vise jaws dont have to be precise by any means... I have a locating slot on the back and the face that locates against the vise face and vise way are perpendicular. aside from that i run them as fast as possible and dont care about taper or any other "issues"
I have a video cutting the vise jaws.
Okuma Genos M560-V Cnc mill & Gibbscam with Volumill - YouTube